Elastic tissue returns to a minimum elastic, or relaxed, state when released from tension. In this relaxed state, tissue cells have a spherical shape, cell walls are thick and strong, and cell surface tensions are minimized and balanced. A cell in this minimum elastic state will remain relaxed, demonstrating behavior similar to a non-elastic material. The force required to elongate a cell in this state often approaches a force that will rupture or sheer intercellular bonds, causing localized failures or tears. Soft tissue in this minimum elastic state provides minimum surface coverage and has the highest reluctance to stretch. It is believed that a gentle but constant force below the sheer force threshold applied to tissue in combination with adequate hydration will, over time, restore the skin to the original elastic state. Additionally, this force can be applied to stretch tissue past the point of equilibrium (normal elastic range) to the maximum elastic range and create the thinnest possible configuration, covering the maximum surface area. If intercellular pressures in the tissue do not exceed the point at which intercellular bonds are compromised, the tissue remains at the maximum elastic state as healthy tissue, and normal biological processes will build additional cells to restore normal skin thickness and tension, which is described below as biological creep.
Plastic tissues, such as skin and muscle, possess certain viscous and elastic rheological properties, and are therefore viscoelastic. Certain plastic tissues are able to increase surface area over time, which is described as “creep.” Mechanical creep is the elongation of skin with a constant load over time, while biological creep refers to the generation of new tissue due to a chronic stretching force. A constant and unrelenting force applied a body tissue, such as skin or muscle, may result in both mechanical and biological creep. Mechanical creep restores the tension originally present but lost in the skin across the incision or wound by retensioning skin or soft tissue cells, thereby increasing skin coverage. Biological creep occurs more slowly and involves the creation of new tissue. Tissue expansion has long been part of the art of plastic surgery, traditionally accomplished with balloon-type tissue expanders embedded under the skin and externally inflated and increased over the to create expanded pockets of skin for procedures such as breast reconstruction after radical mastectomies, and stretching healthy tissue prior to plastic surgery for the creation of flaps for soft tissue closure.
Wound management, including treatment and care of large skin defects and severely retracted incisions, is an area of increasing importance in medicine today. There are many types of wounds and conditions that require treatment, including, but not limited to: diabetic ulcers and other chronic ulcers; venous stastis ulcers; pressure sores or ulcers; burns; post traumatic lesions, such as post disarticulation, post debridement, cutaneous gangrene, post colectomy, crush wounds with ischemic necrosis; collagen disease, including rheumatoid arthritis; vasculitis (lesions and ulcers caused by arterial insufficiency); amputation; fasciotomy; abdominal surgery; post sternotomy; necrotising fasciitis; trauma; wounds having exposed plates or bones; scar revision; skin lesions; bariatric surgery; blunt abdominal trauma with perforations; pancreatitis; neuropathic ulcers; compartment syndrome; and other subacute or chronic wounds. Treatment and care of these defects is challenging due to difficulties in closure of open wounds.
Compartment syndrome is a condition in which increased pressure in a limited space compromises the circulation and survival of the tissues within that space. Elevation of interstitial pressure in a closed facial compartment results in microvascular compromise within the compartment and vascular insufficiency, reducing blood flow. Capsulated internal pressure is created when swelling exceeds the elastomeric capacity of the skin. This condition is commonly caused by capillary infusion following, for example, trauma, inflammation, burns or intense muscle use. As duration and magnitude of interstitial pressure increase, necrosis of soft tissues eventually develops. If left untreated, it can lead to permanent injury to muscle, nerve and vascular structures, resulting in major loss of function, limb, and even life. These types of permanent injuries resulted in amputations prior to the development of aggressive treatments.
Objectives of treatment of compartment syndrome include minimizing deficits in function by promptly restoring local blood flow. This can be accomplished through surgical decompression, which consists of pressure release by an expedient fasciotomy in which each potentially limiting envelope, including skin, is opened over the entire length of the compartment. Expedient fasciotomy provides room for tissue expansion, which results in an instant relief in pressure, restores normal vascular function, and minimizes tissue death that would result from restricted circulation. The skin is left open after surgical decompression to prevent it from becoming a limiting envelope during the anticipated period of post-ischemic swelling. This large, open incision allows the engorged tissues to expand beyond normal dermal restriction and resume normal pressures. Over time, fluid is reabsorbed and tissues return to a pre-trauma size. In many cases, skin closure may be attempted three to five days after surgical decompression by direct suture or meshed skin graft. However, the elastomeric properties of the skin cause wound edge retraction over time, and make closure difficult or impossible. Objectives for closure of other wounds and skin defects are similar to those for closing a fasciotomy.
Two common methods of closure of wounds and skin defects include split thickness skin grafting and gradual closure. A split thickness skin graft involves removing a partial layer of skin from a donor site, usually an upper leg or thigh, and leaving the dermis at the donor site to re-epithelialize. In this manner, a viable skin repair patch can be transferred or grafted to cover a wound area. The graft is often meshed, (which involves cutting the skin in a series of rows of offset longitudinal interdigitating cuts) allowing the graft to stretch to cover two or three times greater an area as well as provide wound drainage while healing. Normal biological function of the skin heals the holes after the graft has been accepted. A meshed graft of this type requires a smaller donor area than a conventional non-meshed or full thickness skin graft. However, these methods do not provide optimal cosmesis or quality of skin cover. Other disadvantages of this method include pain at the donor site, creation of an additional disfiguring wound, and complications associated with incomplete “take” of the graft. In addition, skin grafting often requires immobilization of the limb, which increases the likelihood of contractures. The additional operation and prolongation of hospital stay is an additional economic burden.
Gradual, or progressive, closure is a second method of closure. This technique may involve suturing vessel loops to the wound edge and drawing them together with large sutures in a fashion similar to lacing a shoe. In addition, the wound edges may be progressively approximated with suture or sterile paper tape. The advantages of this gradual, or progressive, technique are numerous: no donor site is required for harvest of a graft, limb mobility is maintained, and superior cosmetic result, more durable skin coverage, better protection from full skin thickness and the maintenance of normal skin sensation may all be achieved.
Existing devices for effecting a gradual closure have many disadvantages. Current methods and devices draw wound edges together using mechanical devices such as screw-actuated devices that require repeated periodic adjustment because a relatively small skin movement substantially eliminates much of the closure force. Widely used existing closure techniques involve use of relatively inelastic materials, such as sutures or surgical tape. Excessive tension may cut the skin or cause necrosis due to point loading of the tissue. Current solutions include suture bolsters, suture bridges, use of staples as anchors at the wound edge, and the use of ligature wire to distribute the load along the wound margins. These approaches all rely on static ribbon or suture material, which must repeatedly be readjusted in order to function effectively, and even with this constant readjustment, maintenance of near constant tension over time is difficult, if not impossible, to achieve. Widely used traditional gradual closure methods rely on static force through fixed distance reduction, and do not provide continuous or dynamic tension.
Many current methods of open wound reduction employ static or non-yielding devices such as sutures or hard approximators, which reduce the distance between the wound margins and rely on the skin's natural elasticity to compensate for movement. One problem with these devices has been that when they are at the point of being most effective, when the skin is at the point of maximum stretch, additional skin tension created through motion, such as breathing or walking, creates stress points where the mechanical fasteners meet the wound margins, causing tearing and wound edge necrosis. This has generally required patients to remain immobile during the course of treatment. Existing systems for treating animals need not consider cosmetic result to such a degree as the healthy patient typically masks the wound site with fur, but cosmesis is a critical criteria in the measurement of a successful result from the system in the human application.
One existing device for effecting closure of a wound utilizes a constant tension, low-grade force to draw wound edges together. This device, the Proxiderm™ system, includes a pair of hooks carried by a pair of sliders that move along a path pulled by a pair of springs. This spring device is enclosed in a plastic housing and is available in four models with different curvature. The sharp hooks used in this system may damage the skin. The constant force used is a dictated force that is not variable.
Other closure devices are described in U.S. Pat. Nos. 5,234,462 and 5,649,960 to Pavletic, which disclose the use of elastomeric material to approximate wound margins, including rubber bands and other types of compressive and non-compressive materials. A kit disclosed by Pavletic requires bonding to the skin with an adhesive and also requires periodic adjustment to tighten the straps. One embodiment uses hooks and elastic loops, which must be replaced with smaller elastic loops to maintain tension. Another Pavletic embodiment uses a motor power source to provide a tightening means. The Pavletic patents do not disclose a system that eliminates the need to adjust the tension repeatedly, or a system that is self-regulating and self-adjusting.
One currently used device is the Sure-Closure device, which consists of two surgical needles, two U-shaped lexan polycarbonate arms with hooks on the bottom surface, a threaded tension bar and a polycarbonate ruler. The needles are threaded along the wound margin, and each arm is positioned above a needle, with the hooks piercing the skin and engaging the needles. The tension bar is then locked, and tension can be adjusted using the screw.
Existing methods of gradual wound closure fail to provide an effective gradual closure that restores original skin tensions lost across the wound. For example, the Proxiderm™ system has a single tension of 460 grams. In many instances, such as with the elderly or with compromised skin, this force is too great, resulting in localized failures, tears and necrosis. Many current devices are cumbersome, restrict patient mobility, must be completely removed for wound dressing and cleaning, and are usable in a relatively limited number of situations because of size constraints. Many also require a surgeon for reinstallation after removal for wound dressing. Finally, current devices cannot readily be used for radial closure of wounds due to their limited ability to pull in a single direction along an overhead beam, thereby restricting their application to parallel pulls along the same axis.
There is a need for a system providing for manipulation and control of tissue tensions on a living person or animal, utilizing both stretch and creep to restore and move plastic tissues. What is needed is a method and device for moving and stretching plastic tissue that is simple, easy to use, relatively inexpensive, extremely versatile, self-adjusting and capable of exerting relatively constant tension over a certain distance and at various intersecting angles in complex geometrical wounds.